How much traffic can Hikashop handle?

Yes, it will indeed depend on your hosting plan. It also depends on how you configure your shop and how well you optimize your website. Caching can help a lot. If you display 300 products on each page of your products listings it's gonna slow down the display of your pages. There are many tools for Joomla to optimize your website.
HikaShop is only one element in all that so it's not possible to give you an accurate figure.

On our end, we do all our possible to make HikaShop as fast and efficient as possible, and we keep improving it.
For example, we're currently working on the cart/checkout system and we hope to increase performances on that end by 50% with the new system, on top of making it more user friendly, more flexible and more bug-proof in several months, when we release the new system.

Hi,

I don't know. We're working on it and we'll release it when it will be ready. It will take many months I expect.